A&P Formatting memory card problem

I took about 250 pictures on Sat for a bday party. I was able to look at all of the pictures, but then out of nowhere the camera showed the blocks were all of the pictures were, but would not show the actually picture (the block were empty). It also began saying that you need to format the memory card (i pressed no).

Can anyone help me out as to what happened and how I can recover / see the pictures? I connected via usb to my comp and it wont show the pics. Im going to try out my memory card reader on my comp later